This invention relates to the field of compact electrically powered heaters mounted in exhaust streams from chemical or manufacturing processes or from engines, both mobile and stationary.
One can use such heaters (a) for bringing exhaust streams up to temperature rapidly under cold start conditions, for emission control, and (b) for holding exhaust streams at sufficiently high temperatures, such that a catalyst can be heated to and held at or above its light-off temperature, where it becomes effective, and (c) for general process heating.
In a particular application of the invention, an electrically heatable cord is close-coupled to a conventional catalyst or catalysts in the exhaust system of a vehicle. The heatable core serves to heat the conventional catalyst during initial cold start conditions, according to a predetermined heating-control strategy, by means of radiative and convective transfer of heat energy.
In a second embodiment of the invention, the heated elements (metal strips) are coated with catalyst materials and can be positioned upstream of a conventional catalyst or catalysts. The light-off of the catalyst adhered directly to the strip is more rapid than in the case above. In this latter case, the heater is known as an "electrically heated converter" (EHC). Descriptions of EHCs appear in U.S. Pat. Nos. 4,928,485, 4,976,929, and 5,070,694. This specification hereby incorporates by reference the disclosures of all of the above-cited patents.
In either the first or the second embodiment of the invention, the new devices trigger the release of chemical energy to provide heat to light-off the main catalyst and maintain the gas stream at the light-off temperature.
In its most general form, the present invention comprises an electrically powered non-catalytic heater which can be used to heat a gas stream.